LeetCode Triangle

Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.

For example, given the following triangle

[
     [2],
    [3,4],
   [6,5,7],
  [4,1,8,3]
]

The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 = 11).

public class Solution {
    public int minimumTotal(List<List<Integer>> triangle) {
        int[] lastsum=new int[triangle.size()+1];
        int[] thissum=new int[triangle.size()+1];
        int sum=Integer.MAX_VALUE;
        if (triangle.isEmpty()) return 0;
        for (int i = 0; i < lastsum.length; i++) {
            lastsum[i]=sum;
            thissum[i]=sum;
        }
        lastsum[0]=0;
        int j;
        for (List<Integer> list : triangle) {
            for (int i = 0; i < list.size(); i++) {
                if (i==0) {
                    j=0;
                }else {
                    j=i-1;
                }
                thissum[i]=list.get(i)+Math.min(lastsum[i],lastsum[j]);

            }
            for (int i = 0; i < lastsum.length; i++) {
                lastsum[i]=thissum[i];
            }
        }
        for (int i : lastsum) {
            if (i<sum) sum=i;
        }
        return  sum;
    }
}